1. Field of the Invention
This invention relates to a pneumatic driven ratchet wrench, more particularly to a pneumatic driven ratchet wrench including a wrench housing with a head section and an operating knob disposed at a position distal from the head section for switching rotational directions of a ratchet wheel.
2. Description of the Related Art
FIG. 1 illustrates a conventional pneumatic driven ratchet wrench 1 that includes a wrench housing 11 with a head section 111 and a handgrip section (not shown), a ratchet wheel 12 mounted in the head section 111, two gear members 13, each of which is selectively engageable with the ratchet wheel 12, a swingable driving link 14, a shaft 15 with an eccentrically disposed head 151 connected to the swingable driving link 14, a cylindrical pneumatic rotor (not shown) connected to the shaft 15 and powered by a compressed air so as to co-rotate with the shaft 15, and a direction-switching unit 16 including a pinion 161 and two racks 162 disposed at two opposite sides of the pinion 161 and engaging the pinion 161. An operating knob (not shown) is connected to the pinion 161, and extends therefrom through the head section 111 of the wrench housing 11 for a user to operate in selecting a desired rotational direction of the ratchet wheel 12. In operation, when the ratchet wheel 12 is to be set to a selected rotational direction, the operating knob is rotated in a corresponding direction to drive the racks 162 to move in opposite directions such that a corresponding one of the racks 162 is moved to engage the ratchet wheel 12 and the other is moved to disengage the ratchet wheel 12.
The conventional pneumatic driven ratchet wrench 1 is disadvantageous in that since the operating knob protrudes outwardly from the head section 111 of the wrench housing 11, the overall profile of the head section 111 is considerably increased, which renders the ratchet wrench 1 unsuitable or difficult for tightening or loosening screws in a narrow space. In addition, since the operating knob is disposed at the head section 111 and since the handgrip section is disposed at a position distal from the head section 111, operation of the operating knob cannot be reached by fingers of the hand that holds the handgrip section.
U.S. Pat. No. 8,051,746 discloses a pneumatic driven ratchet wrench that is powered by a compressed air and that includes a wrench housing having a head section for accommodating a direction selector, a gear set, a yoke, a pawl engageable with the yoke, and a drive body coupled to the direction selector. A collar is mounted to the head section and engages the gear set through a right angle gear so as to cause the ratchet wrench to switch between clockwise and counterclockwise rotations. The ratchet wrench disclosed in the patent has the aforementioned drawbacks.